The present invention is directed to a scrap submergence system of the type typically employed in metal recycling processes, particularly, the recycling of aluminum. In the recycling of metals, it is necessary to melt scrap pieces for treatment and processing. A large portion of the aluminum scrap pieces are thin walled as a result of the mechanical shaping action from which they are formed, such as, shaving, boring and cold rolling. Melting thin walled scrap pieces is particularly difficult because, (i) extended exposure to the hostile atmosphere in a traditional melting furnace results in extremely high oxidation loss and, (ii) rapid submerging in molten metal is severely hampered by the fact that thin walled scrap pieces float on molten metal ("floating scrap").
In a typical melting operation used to convert floating scrap to ingot, a melting furnace is provided with an enclosed hearth and a connected open sidewell. Usually the sidewell is divided into a pump well and a melting bay. A pump or other molten metal flow inducing apparatus is positioned externally to the melting bay (e.g., in the pump well), and causes molten metal to flow from the hearth to the melting bay. Typically the melting bay is further divided into a chargewell and a drosswell. Metal scrap pieces are fed into the melting bay, particularly the chargewell component thereof.
A variety of apparatus have been used in the melting bay (specifically in the chargewell) to facilitate the submergence of the scrap metal below the surface of the molten metal bath. Three major types of systems exist. The first type includes mechanical systems constructed primarily of a rotor which creates a molten metal flow from the top surface. Examples of these devices are shown in U.S. Pat. Nos. 3,873,305; 3,997,336; 4,128,415; and 4,930,986. The second type of system uses a mechanical device to physically push the scrap below the melt surface (elephant feet/well-walkers). The third type of system relies on the shape of the chamber without rotation of a rotor to create a metal flow which submerges scrap pieces in the chargewell. Particularly, the flow of molten metal into the chargewell is manipulated in such a manner to achieve a vortex which draws chips from the top surface into the bath. These systems include, for example, U.S. Pat. Nos. 3,955,970; 3,984,234; 4,286,985; and U.S. Ser. No. 08/784,832, each of which is herein incorporated by reference. The present invention is directed to this third type of scrap submergence system. However, the present invention is directed to a novel system which achieves a high charge rate and a high recovery rate with minimal maintenance requirements (three important requirements).
While the present invention is directed to the third class of submergence devices, the present invention contrasts the traditional design by achieving a vortex with an initially upward flow of metal adjacent the outer walls of the feed bay. In contrast, in U.S. Pat. No. 4,286,985, a chargewell includes a top inlet and a bottom outlet which are positioned to create a downward flow of molten metal adjacent the side walls of the well to form a vortex. Similarly, with reference to U.S. Ser. No. 08/784,832, a chargewell is designed to include a unique wedge positioned on one of the walls of the feed bay to create a downward flow of molten metal and the vortex. In both systems, the intention of the design is to create a downward flow in the molten metal pattern as it circles to form the vortex pattern within the charge well.